Earthworm Sublethal Responses to Titanium Dioxide Nanomaterial in Soil Detected by 1H NMR Metabolomics

H-1 NMR-based metabolomics was used to examine the response of Eisenia fetida earthworms raised from juveniles for 20-23 weeks in soil spiked with either 20 or 200 mg/kg of a commercially available uncoated titanium dioxide (TiO2) nanomaterial (nominal diameter of 5 nm). To distinguish responses specific to particle size, soil treatments spiked with a micrometer-sized TiO2 material (nominal diameter, <45 mu m) at the same concentrations (20 and 200 mg/kg) were also included in addition to an unspiked control soil. Multivariate statistical analysis of the H-1 NMR spectra for aqueous extracts of E. fetida tissue suggested that earthworms exhibited significant changes in their metabolic profile following TiO2, exposure for both particle sizes. The observed earthworm metabolic changes appeared to be consistent with oxidative stress, a proposed mechanism of toxicity for nanosized TiO2. In contrast, a prior study had observed no impairment of E. fetida survival, reproduction, or growth following exposure to the same TiO2 spiked soils. This suggests that H-1 NMR-based metabolomics provides a more sensitive measure of earthworm response to TiO2 materials in soil and that further targeted assays to detect specific cellular or molecular level damage to earthworms caused by chronic exposure to TiO2 are warranted.